Green’s Dictionary of Slang

1. (US Und.) to sell, usu. stolen goods.

1929		E. Booth Stealing Through Life 195: You can ‘turn’ about three cars a month, and they will give you about eight or ten thousand clear.
1969		B. Jackson Thief’s Primer 61: turn: sell (stolen goods).
1973		M. Agar Ripping and Running 164: Turn – Sell.
1986		J. Ellroy Suicide Hill 139: ‘[I]f you turned the pieces, you've got twenty-four hours to give me the names. [...] If I don't hear from you [I] snitch you off [...] as the kingpin motherfucking gun dealer of L.A. County’.

2. (US drugs) vi., vtr., to sell drugs (to); of a doctor or dentist, to write prescriptions for narcotics.

1938		D. Maurer ‘Lang. of the Und. Narcotic Addict’ Pt 2 in Lang. Und. (1981) 110/1: To turn. To consent to sell narcotics to an addict. Also to sail, to write script (when applied to physicians).
2004		J.A. Juarez Brotherhood of Corruption 204: ‘Sarge, that’s a positive and you want the shorty that turned me’.
2006		G. Pelecanos Night Gardener 40: They turned [the dealer’s] product [...] Charles’s people sold dimes in small plastic bags.